A nerve plexus is a network of intersecting nerves; multiple nerve plexuses exist in the body. Examples include: the cervical, brachial, lumbar, sacral, celiac, and coccygeal plexuses. The plexus is the characteristic form of nervous system in the coelenterates and persists with modifications in the flatworms. The nerves of the radially symmetric echinoderms also take this form, where a plexus underlies the ectoderm of these animals. Deeper in the body other nerve cells also form plexi of limited extent.
The cervical plexus serves the head, neck, and shoulders and is formed by the ventral rami of the upper four cervical nerves and the upper part of fifth cervical ventral ramus. The network of rami is located deep within the neck. The brachial plexus serves the chest, shoulders, arms and hands and is formed by the ventral rami of C5-C8-T1 spinal nerves, and lower and upper halves of C4 and T2 spinal nerves (Figure 2). The plexus extends toward the armpit (axilla). The lumbar plexus serves the back, abdomen, groin, thighs, knees, and calves and is formed by the ventral rami of L1-L5 spinal nerves with a contribution of T12 form lumbar plexus (Figure 1). This plexus lies within the psoas major muscle. The sacral plexus serves the pelvis, buttocks, genitals, thighs, calves, and feet and is formed by the ventral rami of L4-S3, with parts of L4 and S4 spinal nerves. It is located on the posterior wall of pelvic cavity.
The coccygeal plexus serves a small region over the coccyx and originates from S4, S5, and Co1 spinal nerves. It is interconnected with the lower part of sacral plexus. In addition, the celiac plexus serves the internal organs and Auerbach's plexus serves the gastrointestinal tract.